Re: magnets in HDs

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-qwest-dot-net>" <evp-at-pacbell-dot-net>

Tesla list wrote:
> 
> Original poster: "Mr Gregory Peters by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <s371034-at-student.uq.edu.au>
> 
> After reading the post on magnets in hard drives, I was somewhat
> skeptical - after all, don't magnets ERASE hard drives? Anyway, I
> decided to pull apart an old 1 Gb SCSI hard drive I had lying around. It
> was difficult to find, but there is definitely a strong magnet in there.
> It is near where the read/write head "arm" connects to the HD chassis.
> It seems to be in some sort of "anti-magnet" metal enclosure, as I could
> not detect it at all with a screwdriver until I pulled it completely
> apart. It is very strong. There was only one magnet in this drive, but I
> reckon if I had two magnets I would not be able to pull them apart. The
> magnet is arc shaped, about 1.3" long x 0.5" wide x 0.2" thick. I would
> love to know what kind of magnet it is if anyone knows.
> 
> Cheers,
> 
> Greg Peters

	That is a head drive motor.  The magnetic field is pretty well confined
by the magnetic circuit so leakage is not a problem.  The usual name for
the material is Neodymium-Iron-Boron, but the iron and boron are
sometimes interchanged in describing them.  Very neat stuff, with a very
high energy product.

	A story about disk drives.  At one time where I work there were a bunch
of the old giant IBM drives with removable disk packs.  Since they had
been used with highly classified data the security department had them
locked up.  Those guys aren't engineers and didn't realize that the
drives without the platters didn't contain any info at all, so decided
to trash the whole lot.  One of my friends came across remains of the
last of the lot in a dumpster, and salvaged four of the largest NIB
magnets I have ever seen.  About 2.5" by 2" by almost 3/4" thick.  Can't
imagine what they cost originally.  Anyhow, Glenn got em out and brought
them to my office to show me.  We stuck one to an ordinary steel filing
cabinet (thin metal, easily saturaged) and it took us an hour to get it
loose.  We had to slide it to one edge of the cabinet and work it loose
there, as there was no way of pulling it up off the surface.  I would
guess the force was well over a hundred pounds.  Glenn later stuck the
two together in a fit of madness, and as far as I know they are stuck to
this day.

	In handling those magnets you have to be very careful, as the material
is quite brittle.  Aside from any finger pinching you may encounter if
you let two of them snap together there is a good possibility one or
both will shatter.

Ed